[bikerhifinut]

I use a pair of Quad ESL989 in the main stereo system, very nice loudspeakers especially for my tastes.
Now as a rule I only use either one of my Valve power amplifiers which vary from a 35W kit KT88 design through a home brew 30W EL34 design down to my beloved old Leak stereo 20. All of which cope handsomely.
The solid state amps I am happy to use are either the Quad 405 (of course!) and an old Mitsubishi 50Watt power amp. The Mitsubishi can get flustered when pushed and I only feel safe using it because its output protection circuits function well.
So far so good.
So the question is this, what output circuits are OK to use, mainly on older gear as I reckon modern kit will have output protection built in if its been designed properly.
I am aware of certain NAIM amps having self destruct abilities into difficult and capacitive loads so we can dismiss those.
I was curious as I would be interested in listening to the refurbed Rogers Ravensbrook via the quads but it has no active speaker protection circuit, merely a Zobel network across the output and a 1A fuse on the power supply after the rectifiers/reservoir capacitor.
The output stage is transformer coupled to a pair of TO3 transistors in pushpull, capacitor coupled to the speakers. I suspect they are a version of the 2N3055, on this amp Rogers used "specially selected" Solitron SDT9210 but different production runs used different types from different manufacturers which is why I suspect they are just 2N3055 equivalents selected and matched.
I have tried to paste a copy of the output circuit into this post.
So will I do a nasty to the output stage connecting to a pair of ESL? They seem to need around 5watts on them to provide a reasonable level, they are very insensitive.

Andy